וּבְנֵ֣י קֵינִי֩ חֹתֵ֨ן מֹשֶׁ֜ה עָל֨וּ מֵעִ֤יר הַתְּמָרִים֙ אֶת־בְּנֵ֣י יְהוּדָ֔ה מִדְבַּ֣ר יְהוּדָ֔ה אֲשֶׁ֖ר בְּנֶ֣גֶב עֲרָ֑ד וַיֵּ֖לֶךְ וַיֵּ֥שֶׁב אֶת־הָעָֽם׃
And the children of the Kenite, Moses’father-in-law, went up out of the city of palm-trees with the children of Judah into the wilderness of Judah, which is in the south of Arad; and they went and dwelt with the people.
Shenei Luchot HaBerit
Cain and Abel were the first men born by woman. They were intended to be the typical "אדם" i.e. representative of what mankind should develop into. Now it had become the turn of the people of Israel to be refined and to acquire the appellation "Adam." According to our Kabbalists, Moses was the re-incarnation of Abel, הבל, whereas Yitro was the re-incarnation of Cain, חבר הקיני (see Judges 1,16, Zohar 3,216).